For the ATxmega chips the getchar and putchar functions use by default the USARTC0.
If you wish to use another USART, you must define the _ATXMEGA_USART_ preprocessor macro prior to #include the stdio.h header file, like in the example below:


/* use the ATxmega128A1 USARTD0 for getchar and putchar functions */
#define _ATXMEGA_USART_ USARTD0


/* use the Standard C I/O functions */
#include <stdio.h>


The _ATXMEGA_USART_ macro needs to be defined only once in the whole program, as the compiler will treat it like it is globally defined.

All the high level Input/Output functions use getchar and putchar.